This achievement is also solo-able.
*Simply start a Private Rescue Match.
*Make sure your a survivor, not Solarii.
*Put the Number of Medkits to Retrieve to 20 instead of 5.
You can adjust the round time limit as well, but 10 minutes is just enough time to retrieve all 20 Medkits on the Beach map.
*A soon as you get all 20 Medkits and the round is over. Wait until the post game lobby comes up. You can now leave and re make the lobby and start over.
"Make sure your loadout includes the Second Wind offensive skill and then hold cn_B to sprint when you head out to find the kit, which will speed thing up somewhat. Unfortunately, you can't sprint once you have the kit." ~~ Runner7922
This method can also be used to get tons of salvage on the Beach map. I averaged 30,000 exp when retrieving 20 Medkits as a Survivor in under 10 minutes and I averaged 26,000 salvage every 20 minutes as a Solarii ( rope ascender makes it stupid fast ).
This method will take a little over 10 hours to achieve Level 60. (Thanks Uncle BAZINGA
I'll post a video soon on my actual game play.